Blastocyst Implantation & Pregnancy — NEET Biology
✅ Asked in NEET 2023The morula continues to divide and transforms into blastocyst as it moves further into the uterus. The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus. This is called implantation and it leads to pregnancy.
NTA tests whether you understand implantation: how the blastocyst embeds in the uterine endometrium after trophoblast attachment, triggering pregnancy. Students often confuse the sequence—they mistake when the blastocyst divides into trophoblast and inner cell mass, or forget that the endometrium actively grows around the blastocyst during embedding. Key to remember: implantation occurs AFTER the blastocyst reaches the uterus, the trophoblast attaches first, uterine cells proliferate to cover it, and only then is pregnancy established. This concept is foundational for understanding early embryonic development and reproductive physiology.
Assertion A: Endometrium is necessary for implantation of blastocyst. Reason R: In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium.
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